1. Field of the Invention
This disclosure is directed to a liquid crystal thermoset (“LCT”) monomer or oligomer, a thermosetting liquid crystal polymer composition including the LCT monomer or oligomer, and a printed circuit board using the LCT monomer or oligomer. More specifically, the LCT monomer or oligomer is terminated with methylmaleimide. The presence of the terminal methylmaleimide in the LCT monomer or oligomer allows for the production of a printed circuit board with excellent characteristics in terms of flame retardancy, heat resistance and mechanical properties.
2. Description of the Related Art
Recent advances in information and communication technologies have transformed our society into a high-tech communication and information society. The trend toward miniaturization and high performance of electronic devices, for example, mobile phones and personal computers, has led to high-density integration of printed circuit boards as essential elements of the electronic devices. Such high-density integration is mainly achieved by layering printed circuit boards, reducing the thickness of printed circuit boards, making the diameter of through-holes smaller and reducing the interval of holes. Under these circumstances, there is a need for novel board materials that offer higher performance.
The use of high operating frequencies for rapid processing of large amounts of information in electronic information devices such as computers involves problems of transmission loss and signal delay. Generally, a signal delay in a printed circuit board increases linearly with the square root of the relative permittivity of an insulating material around interconnection lines. Thus, low-permittivity board materials are needed to produce printed circuit boards requiring a high transmission rate.
Liquid crystal polyester resins are board materials that have a dielectric constant as low as 3.0 and exhibit excellent characteristics, such as high heat resistance and low moisture absorption. The production of printed circuit boards using liquid crystal polyester resins is dependent on melting processes, such as injection molding, because most of the liquid crystal polymers are insoluble or slightly soluble in solvents. However, injection or extrusion of a liquid crystal polymer resin for the production of a printed circuit board renders the polymer highly anisotropic due to the orientation of the polymer chains, causing difficulty in designing a circuit. Further, the use of a liquid crystal polymer in a molten state for the production of a prepreg has the problem that impregnation of the liquid crystal polymer into a glass fiber doe not occur. In an attempt to solve this problem, a method was reported in which a solution of a liquid crystal polymer is cast to produce a film or prepreg. The solubilization of the liquid crystal polymer, however, requires a reduction in the number of constituent mesogen groups in the liquid crystal, which leads to a decrease in the glass transition temperature of the film or prepreg, which is indicative of poor heat resistance.